Polymers which are either compression molded or injection molded rarely present the combination of properties that one would wish to encounter, particularly a good resistance to atmospheric aging. Usually during the course of time, regardless of whether they are thermoplastic or thermosetting, the pigmentation and mechanical properties of the polymers are altered by the action, among other things, of ultraviolet rays and of corrosive atmospheric agents.
However, polyvinylidene fluoride (PVF.sub.2) is known for its properties of resistance to ultraviolet rays and to corrosive chemical agents, which are peculiar to fluorinated resins, and so it has long been desired to use these properties of fluorinated resins for the protection of other polymers. The implementation of this idea has, however, never been able to be put into practice on molded polymers which are incompatible with PVF.sub.2 because of another property of the latter, which in the present case is a drawback; namely, the non-adherence to incompatible polymers.
It has been considered to protect parts after molding by gluing a sheet of PVF.sub.2 onto them. Besides the fact that this technique requires a complex manipulation, the result obtained is only imperfect and exhibits the drawbacks inherent in gluing processes which in time are manifested in incidents of ungluing (detachment).